1. Field of the Invention
The present invention relates to an element mounting substrate.
2. Description of the Related Art
Recently, a cell-phone, a small computer, and so on are required to be further miniaturized, accordingly a semiconductor device and a semiconductor module are reduced in weight, thickness, length, and size. In a set incorporating the semiconductor device and the semiconductor module, many ICs are incorporated into a limited small volume, and therefore, a heat dissipation problem occurs. Further, since the semiconductor device and the semiconductor module aim more functions and a higher current in the small volume, the heat dissipation problem occurs.
Hereinafter, the conventional structure will be described with reference to FIG. 7.
FIG. 7 illustrates a semiconductor device 100 employing an element mounting substrate comprising a metal core. FIG. 7A is a plan view of the semiconductor device. FIG. 7B is a cross-sectional view along A-A′ line of the semiconductor device. The element mounting substrate employs a metal core 101 at the center as the core, and the front surface side is coated with an insulating resin 102A, and the rear surface side is coated with an insulating resin 102B. In the element mounting substrate, conductive patterns 103A and 103B are provided respectively on the insulating resins 102A and 102B. In this case, there is provided a double-layered structure in which the insulating resin layers 102A and 102B and the conductive patterns 103A and 103B are formed on the front and rear sides; however, the conductive patterns may be further stacked to provide a four-layered structure, a six-layered structure, or more.
A semiconductor element 104 such as an LSI is secured to the element mounting substrate through a solder ball 106 formed corresponding to the conductive pattern 103A, and an insulating resin film 105 seals to cover the semiconductor element 104 while remaining a periphery of the element mounting substrate, whereby the semiconductor device 100 is formed. The semiconductor device 100 employing the element mounting substrate comprising the metal core thus has the effect of diffusing heat generated from the semiconductor element 104 through the metal core 101 and thereby reducing the temperature of the semiconductor element 104.
In FIG. 7, in order to reduce the thickness of the entire semiconductor device 100 as much as possible, the semiconductor element 104 is made face-down to be mounted. In this case, the heat emitted from the semiconductor element 104 is emitted to the metal core 101 through the solder ball 106 and the conductive pattern 103A, so that the temperature of the semiconductor element 104 is less likely to be reduced. Namely, since the flow of heat from the semiconductor element 104 is regulated by the solder ball 106 which is a neck portion, the temperature of the semiconductor element 104 is less likely to be reduced.
FIG. 8 shows a semiconductor device (semiconductor module) mounted with the semiconductor element.
FIG. 8A shows a structure of a semiconductor module 100A mounted with the face-up semiconductor element 104. Because of the face-up mounting, the thickness of the semiconductor module 100A itself is increased by the height of a thin metallic wire 107. However, in comparison with the case where the rear surface of the semiconductor element 104 is connected to the element mounting substrate by the solder ball, the semiconductor element 104 is secured in a larger area, and therefore, the temperature of the semiconductor element 104 is significantly reduced in comparison with the case of mounting the semiconductor element in FIG. 7.
FIG. 8B shows a semiconductor module 100B that is not coated with the insulating resin film 105, and passive elements such as a semiconductor element and a chip capacitor are mounted on the element mounting substrate. In the present view, although the semiconductor element 104 is secured using the thin metallic wire, the semiconductor element 104 may be secured through a bump as shown in FIG. 7.
As described above, when a heat radiation property is required in a slimline package and a module employing a substrate, a metal core substrate is preferably employed. However, as the metal core, Cu is mainly employed, and the thickness is approximately 250 μm to 500 μm. Accordingly, in a double-layered conductive pattern and a four-layered conductive pattern, the thickness is approximately 1 mm, and therefore, the metal core is easily plastically deformed. Once a metal is plastically deformed, the metal cannot be returned to the original shape unless it is deformed again in the opposite direction, and therefore, this leads to reduction in yield in a manufacturing process. In finished products, the reliability may be reduced. Further, a difference of a thermal expansion coefficient α between an insulating resin and Cu causes warpage. The warpage is generated in a direction shown by the curved arrow in FIG. 8. In addition, each thermal expansion coefficient is different depending on materials. For example, the thermal expansion coefficient of the insulating resin film is 10 to 15 ppm, the thermal expansion coefficient of the substrate is 13 to 15 ppm in the X and Y directions and 23 to 33 ppm in the Z direction, and the thermal expansion coefficient of Si is 2.5 ppm. Thus, the reliability of the semiconductor element itself is reduced. Accordingly, substrate that can maintain the flatness as much as possible is preferably used.